US2382353A - Method of chlorinating rubber - Google Patents

Description

Patented Aug. 14, 1945 UNITED STATESPATENT OFFICE Henry L. Tomkinson, Sayreville, N. J. assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware i No Drawing. Application December 31, 1942,

' Serial No. 470,833

4 Claims.

This invention relates to chlorinated rubber and more particularly it relates to chlorinated rubber of improved compatibility with alkyd resins.

In the production of many of the difierent types of coating compositions containing chlorinated rubber, it is necessary that the chlorinated rubber be compatible with alkyd resins of which the coating compositions are comprised. Little difliculty has been encountered in obtaining the desired compatibility in chlorinated rubbers of low viscosity such as below 15 centipoises. Considerable difiiculty has, however, been encountered in obtaining satisfactory compatibility in the higher viscosity products which are used where flexibility is needed.

Chlorinated rubber of above 15 centipoises viscosity has heretofore had a limited tolerance for alkyd resins and conversely alkyd resins have had a limited tolerance for chlorinated rubber. General compatibility permitting formulation of coatings containing high proportions of both, for example, coating compositions with a 1:1 ratio of alkyd resin to chlorinated rubber, has not been obtained. In the few cases in which fair compatibility in the higher viscosities has been obtained, it has not been reproducible from batch to batch. Complete and dependable compatibility, i. e., compatibility in films consisting of equal parts chlorinated rubber and alkyd resins, has been desired for the more fiexiblechlorinated rubber of above 15 centipoises.

, Now in accordance with this invention,-chlorinated rubbers having a viscosity of over 15 centipoises and having uniform and improved compatibility With alkyd resins are produced in the f ollowing manner:

Rubber is dissolved in a solvent substantially inert to chlorine to form a 1% to 6% solution, and chlorine is passed into the solution. The solution is heated to an elevated temperature, i. e., above 30 C. but below 76 C., by external heat or the heat of reaction and remains at the elevated temperature throughout the chlorination. The chlorine is added at a rate sufiicient to heat the solution and preferably at least the rate at which the solution can absorb it. Heat is removedv from the solution at the rate required to hold it in the desired temperature range. Chlorination is continued to a point at which a distinct changein the nature of the'reaction ocevolved by the solution and by a dropinthe rate of heatformed by the reaction. Where rate of heat extraction is held substantially constant as the reaction change is reached, there is a drop in temperature of the solution. In some 'cases, dependingon the temperature, there is a sharp change in apparent viscosity due to a change in phase composition of the reaction solution.

Upon reaching the change in reaction characterized by the drop in'heat evolution, a gas containing free oxygen is passed into the mass concurrently with chlorine. It is essential inthe process of this invention, that chlorine be passed into the solution concurrently'with the oxygen.

, Addition of oxygen has the known effect of reducingviscosity. In the present process, the oxygen is added at such a rate that the viscosity is reduced to the desired level, above centipoises and usually below 28 centipoises, before completion of the chlorination and addition of oxygen must I be discontinued prior to completion- The addition of chlorine alone is then continued until the desired chlorine content is attained at a level of at least 64%.

The improvement in compatibility obtained in the present invention is brought about by the continued chlorination with chlorine free of oxygiven to more fully illustrate its specific operation.

3 Ezrample 1 A batch of 400 grams of milled crepe rubber was dissolved in. carbon tetrachloride in a jacketed, closed vessel 'provided with agitator and suitable gas inlets and outlets, the amount of the "solvent being such as to give a. 3.5% concentration of rubber in solution. The temperature of the solution was raised to C. and chlorine was added, with cooling and temperature control at 70 C. by use of water in the vessel jacket, at the rate of 250 grams per hour for four hours. At the end of four hours, the temperature suddenly dropped to 66 C. At this point the chlorine flow was cut to grams per hour and the mixture was -also subjected to a current of air which flowed through the rubber mass at an average rate of 16.8 grams per hour. The addition of two hours.

the air and chlorine together was continued without interruption until the chlorinated rubber obtainable from the mass upon completion of the chlorination had a viscosity of 22 centipoises. The chlorinated rubber attained this Viscosity after the, addition of chlorine and air had been [continued for 2 hours. At this point, the addition of air was discontinued. The flow of chlorine was increased to 200 grams per hour and was gradually decreased again until at the end of the chlorination process (when the chlorinated rubber had a chlorine content of 67% by weight) the a flow had been reduced to '75 grams per hour. The

chlorinated rubber was then recovered by immediate precipitation with boiling water, washing and drying. The material had a viscosity of 22 centipoises and was compatible with alkyd resins.

Example 2 Another chlorinated rubber of excellentco-mpatibility and of comparatively high viscosity was producedin much the samemanner as described in Example 1. Inthis case, however, the chlorine treatment of the 3.5% concentrated solution of 400 grams milled rubber in carbon tetrachloride Was'carried on at a temperature of 65? C. instead of 70 C. When the chlorine had been added at the rate of 250 grams per hour for four hours, the temperature of the treating solution suddenly dropped to 60 C. At this point, as in Example 1, the chlorine flow Was cut to 100 grams per hour and air was added concurrentl'y'at the rate of 16.8 grams per hour until the chlorinated rubber obtainable from the completely chlorinated mass had a viscosity of 25. centipoises. The total time of the concurrent addition of air and chlorine required to lower the viscosity was The addition of air was then discontinued and the chlorine flow was increased 130 200 gramsper hour. The rate of chlorinefiow was gradually reduced until the chlorination was complete. The final chlorinated rubber had a chlorine content of 67 .5%.\by weight. Bythe time the chlorination was complete, the chlorine flow had been reduced to '75 grams per hour. The' product had a viscosity of 25centipoises and wide compatibility with alkyd resins.

Example 3 The chlorinated rubber prepared in this example was prepared in the same manner as in Example 1, except that the chlorination was carried out at 55 C.-instead of at 70 C. It was carried out ona batch of the same size and type as there used. The chlorine wasadded at the rate of 250 grams per hour for 3 hours when the temperature dropped suddenly to 52 C. At this point, the chlorine fiow was reduced to 100 grams per hour and air was added concurrently with the chlorine without interruption until the viscosity of the chlorinated rubber obtainable from the mass upon completion of chlorination was 26 centipoises. The time required for the concurrent addition of air and chlorine was 2 hours. When the desired viscosity was achieved, the addition of airwas discontinued and the chlorination continued. The chlorine flow was increased to 200 grams per hour and then gradually decreased again. When the chlorinated rubber had a chlorine content of 66.5% by weight, the chlorination was discontinued. At the'time when the chlorination was discontinued, the-chlorine flow had been reduced to 75 gramsper hour.

The product had a viscosity of 24 centipoises and wide compatibility with alkyd resins.

Example 4 The chlorinated rubber prepared in this example was prepared at 50 C. The chlorine was passed through a 3.5% solution of 400 grams of the rubber in carbon tetrachloride at the rate of 250 grams per hour, for 3 hours at this temperature. At the end of 3% hours, the temperature of the rubber solution suddenly dropped sharply to 47 C. At this point as in the other examples, the chlorine flow was cut to 100 grams per hour and a flow of air was added concurrently at the rate of about 16.8 grams per hour until a viscosity of 25 centipoises was attained for final chlorinated rubber obtainable from the mass. The air and chlorine were added concurrently for a period centipoises.

The chlorinated rubber products of the examples were tested for compatibility each separately with the following alkyd resins which are believed to be glycerol phthalate condensates with fatty oil acid or resin acid modification, and found to be completely compatible in the 1:1

. ratio:

Duraplex 0-45 Duraplex 0-48 Rezyl 4 12. Bakelite XR3180 Rezyl 807 Amberol 801 The products were also found to be, compatible with methacrylate polymers in the same manner.

The resins were combined with the chlorinated rubbers by dissolving equal parts of the chlorinated rubber and the alkyd resin in xylol and permitting a film to dry therefrom. Both solutionand film must be homogeneous with freedom from blushing, clouding or separation for compatibility. The product of the process according to this invention is characterized by complete compatibility in 1:1 ratio with drying type drying oil acid modified glycerol phthalate alkyd resins, Rezyl 807 serving satisfactorily for test purposes.

Although the above examples have shown that the process in accordance with this invention may be carried out at temperatures of 50-'l0 C., and indeed it may-successfully be used at temperatures as low as 30 C. and as high as 76 C., it is preferred to carry out the treatment attemperatures above 60 C. As disclosed'in U. S. Pat- Rezyl 829 Glyptal 2454 ent 2,182,456, when the chlorination process is point, the mass underchlorination with cooling suddenly drops severali degrees in temperature and. nearly ceases" to evolve hydrochloric acidwhich up tillthis point had been given 'ofi in large volume.' The rate of chlorine absorbed from an excess of chlorineyalso' drops sharply.

There is noapparent-change-iii physical" state of the solution.

The temperaturedrop 'and the other ch'anges occur when the chlorine content of the chlorinated rubber'is between45% and 59% of thetotal weight of the product, usually between 48% and 55%. Thus, even when the chlo'rination is carried on at temperatures above63 Cpwhere' no break" occurs, the most advantageous tiniefor beginning addition of the oxygen is determinable in accordance with this inventionby a decrease in heat evolution whichis indicated by atemperature drop under conditions'of substantially constant cooling, by a decrease in rate of chlorine absorbed, and by adecrease in evolution of hydrogen chloride. The "addition of oxygen conly-after the temperature drop. The period during which oxygen (which may be in the form of air) is added will: vary any where from five minutes toeight hours"'and usually will be from aboutone hour tof three hours. Thus, 'for example; it will vary with the temperature at which the process is carriedoutj the rate of oxygen and chlorine flow, and the viscosity level desired, and the viscosityof the rubber. j, The rate of flow of chlorinei nto the solutipn will usually vary during thediiferent stages of the chlorination procedure as'fseen inf thefex-r amples. Thus,.the flow may be as highias 250 parts by weight per hour or aslow as one part taining gas is best started immediately or short-' by weight per hour foreach 100 parts by weight of rubber. In general, chlorine is addedat the rate at which it canb consumed atthe par r ticular stage and under the particular reaction conditionsinvolved, or in small excessthereover.

The now of air may be varied widely. ,Ratios between'about 0.15 and about 30parts bylweight per hour per 100 parts'by weight of rubber'have been found suitable. Bestfresultsare obtained at airrates between 0.15 and 4.5,parts per hour per 100 parts rubber. Where a source of oxygen richer in oxygen than air isused, be lower to obtain an oxygen supply equivalent to that in air. Thus for pure oxygen the rate is one-fifth of that forair U 1 l It has been mentioned:that the o y entcontaining gas should be added concurrently with a flow of chlorine. This is essential toiinsure. obtaining a product compatible with fatty oil acid-modified alkyd resins. Chlorine should be added at all times air oroxygen is being added at a rate atleast twice that of the oxygen by weight based on pure oxygen. Continuous addition of the air or oxygen for the entire period of addition is highly desirable. Any in'terruption of either gas adversely affectscompatibility the rates may effect isminimized if an interruption, aslfor sampling, is of bothchlorineand oxygen, taking care that all additionof the two gasesaislicom current between the beginning and end of oxygen treatment. l a

It has alsobeen found "that-addition of air or other form of oxygen must bediscont'inued be fore the end of the chlorination to obtainuniform compatibility. Thus sufficient air-must be added during the critical period tocbring the viscosity of the; chlorinated rubbertothe desired level before the chlorination has been completedui The desired level is indicated by the reaction dope viscosity which has a readily determined relation to the final product viscosity at any given. concentration and temperature at this stageof the reaction. Addition .of air must be complete: at a pointat which the chlorinated rubber has a chlorine contentat least 2% less than the chlorine content of the final product; for widest compatibility addition of air. should be complete when,

the material has at least 5% less chlorine than its ultimate product. Oxygen addition will bediscontinued before the chlorine. content reaches 65 and-chlorination is continueduntiluachlorine content at least 2% higher and betweenabout 64% and about 370%, in some fewcasesas high as about 75%, is reached .Chlorination'during the period following. th T critical reaction .change point hereinabove described is relatively slow.

However, after a time a reversal of the change occurs. The mixture regains its reactivity and chlorination to above 64%, which is necessaryto obtain a stable andcompatible product, is then readily achieved. l V l f r In place of air, gases oflhigher oxygen content may'be used. Thus oxygen or ozone may be ride have been found suitable.

used. It is to be understood that when gases con taining a higheroxygen' content thanair' are used, the treatment will require less time or the rate of How of oxygen containing gas will be reduced proportionately. v

lthough it is preferred touse carbon tetrachloride as the solvent for the rubber to be chlor inated, other solvents may be used. Thus, forex-. ample, benzene, chloroform and ethylene dichlo- The rubber utilized may be white crepe, smoked sheet or the like. Preferably, it is milled or otherwise treated to'improve solubility. Preferably, it is first digested, for example, as "described in-the J. M. Peterson U. S. Patent 2,252,728 to i'mproveits suitability for chlorination.

It is to be understood that this process will be applied to produce chlorinated rub'bers having a viscosity of more-than 15 centipoises.- Otherprocesses may be used-to produce uniformlyhigh com; patibility chlorinated rubbersif the viscosity is thereby reduced below 15 centipoises. Chlorinated rubbers with 'viscositiesJoi above l5 centlpoises, which are prepared in accordance with thisdnvention, will have a dependable and uniformly high degree of compatibilitywith a widerangeof alkyd resins not attainable heretofore. The great est compatibility with the widest range of alkyds will beobtained if the process in accordance with this invention is employedto produce chlorinated rubbers with viscosities of less than 2l8 centipoises; preferably 20-27 centipoises. -The process may; nevertheless, be advantageously applied in pro ducing chlorinatedrubbers with viscosities of over 28 centipoises as they will havea hi'gher degree of compatibility although not complete compati= bility with alkyd'resins than chlorinated rubbers produced by other methods known to the art.-

.,-;The: combination of: higher v'iscositi'es and higher compatibility with alkyd resins possessed bychlorinated rubbers preparedin I accordance .Wlt'hlthiS invention is .of value. in. preparing coating compositions in which appreciable proportions of both chlorinated vrubber and alkyd resins are desired.v Previously only very low viscosity chlorinated rubber, which is less flexible; could be :used. The viscositiescof the products referredto in this specification and in the a claims appended gen inthe air by'weight, :the'rate of air addition being sufliciently high toreduce the viscosity to the'walue desired before the chlorinated rubber reaches a chlorine :content :of 64% and before chlorination has been completed; discontinuing addition: of :the air;.continuing Y addition of chlorine1until the chlorine content of the chlorinated rubber; has been increased aminimum of 2% to between 64% and.75%'; and recovering the resulting chlorinated'rubber from the solution.

. 3-1 A process-ofproducing chlorinated rubber of a'viscosity. above 15 centipoises and below 28 centipoises of, improved compatibility with alkyd resins which comprises dissolvingrubber in carbon tetrachloride; passingchlorine gas into the solution thus obtained, ;while extracting heat and tipoises and of improved compatibility with alkyd tweenabout 45% and about 59% and thereoccurs a sudden drop in the ratevof heat evolution by the reaction'iwith an accompanying decreas in the 'rate of reaction of the chlorine, indicating a change in the natureof thereaction'; passing gas containing free oxygen into the solution concurrently with chlorine during a period following the said reaction change until the viscosity of the chlorinated rubber recovered from the solution is reduced thereby to the desired value above 15 centipoises but below 28. centipoises; the rate of chlorine addition during the period .of concurrent addition with oxygen being substantially reducedas compared with itscprevious ratelofaddition and being approximately that at which the chlorine can be absorbedby the rubber solution, the rate of chlorine addition during-theperiod of concurrent addition with oxygen being at alltimes at least twice that of the oxygen by weight based on pure oxygen, the rate of oxygen addition being sufficiently. high to reduce the viscosity to; the value desired before chlorination has been completed; discontinuing addition of the gas containing free oxygen and continuing additionof chlorine alone until the chlorinated rubber is increased in its chlorine content by, aminimum of 2% to acontent in excess of 64% but not above 75% and,

chlorination to the desired extent is completed. 12. A process of producing chlorinated rubber of a viscosity above 15 centipoises and below 28 centipoises and of improved compatibility with alkyd resins which-comprises dissolving rubber in carbon tetrachloride; passing chlorine gas :into the solution thus obtained while maintainingthe solution at 30-76" C. until the chlorine contentof thepartially chlorinated rubber is between about 45% and about, 59%-,and there occurs a sudden dropyin rate oflheat evolutionwith an accom panying decrease in the rate of reaction of. the chlorine, indicating a change in the reaction; passing airthrough the solution concurrentlyand continuously with chlorine during a periodic lowin thesaid reactionchangeuntil the viscosity of the chlorinatedrubber recovered from the solution reaches thedesired value between 15 and about 28 centipoises, the rate of chlorine addition during the periodof concurrent addition-with air being substantially reduced as compared with its previous rate Ofzaddition and being approximately that at which the chlorine can be absorbed by the rubber solution, the rate of chlorine'additionrduring the period of concurrent addition with air being. at all times at least twice thatiof theoxy-.

thereby holding the temperature of the solution substantially constant at between 30 C. and 76 0., during the :major portion of a first stage of reaction, until the chlorinecontent of the partially chlorinated rubber is between about 45% and about 59% and-a sudden drop in temperature accompanied by a ,drop in ability to absorb chlorine indicates theend of the first reaction stage; passing gas containing free oxygen through the solution continuously and concurrently with chlorine during a period substantially immediately following the end of the first stage until the viscosity of the chlorinated rubber recovered from the solution is between 15 and about 28 centipoises, the rate ofchlorine addition during the period of concurrent addition with oxygen being substantially reduced as compared with its previous rate of addition and being approximately that atiwhich the chlorine can be absorbed by the rubber solution, the rate of chlorine addition during the'period of concurrent'addition with oxygen being at all times at least twice that of the oxygen by weight based .on pure oxygen, the rate of oxygen addition being sufiiciently high to reduce the viscosity tothe desired level before the chlorinated rubber has a chlorine content of 64% and before chlorination vhasbeen completed; discontinuing the addition of the gas containing free oxygen; and continuing addition of chlorine until the chlorine content of the chlorinated rubber has increased a minimum of 2% to between 64% wac 4. A p'rocessof producing chlorinatedrubber of a viscosity between about 20 and 27 centipoises and of improved compatibility with alkydresins which comprises dissolving rubber in carbon tetrachloride; passing chlorine, gas into the solution thus' obtained, while extracting heat and thereby holding 'thetemperature of the solution substantially constantat between 60. C. and 70 C. during the'major portionof a first stage of reaction, until the chlorine content of the partially chlorinated rubber is between about 45% and about 59%. and a sudden drop in temperature accompaniedbya drop in ability to absorb chlorine indicates the end of the first reaction stage; passing air into the solution at a rate between about 0.15 and about 30 parts by weight per hour per part of rubber, concurrently with chlorine during a period immediately following the end of the first reaction stage until the viscosity of the chlorinated rubber recovered from the solution is between 20 and about'2'7 centipoises, the rate of chlorine addition during the period of concurrent addition with'air being substantially reduced as compared with its previous rate ofaddition and beingrapproximately that at which the chlorine canFbe absorbedby the'rubber solution, the rate of'chlorine'addition during the period ,of concurrent addition with air being at all times at least twice that of the oxygen in the air by weight, the rate of air addition being sufliciently high to effect the drop to the desired viscosity level before the chlorine content of the chlorinated rubber reaches 64%; discontinuing the addition of air,

continuing the addition of chlorine at a rate at least as high as the rate at which it can be absorbed until the chlorine content of the chlorinated rubber has increased at least 2% and has reached a value between 64% and 70%, and recovering the chlorinated rubber from the solution.

HENRY L. TOMKINSON.